American engineer and inventor William L. Emmet graduated from the Naval Academy and served two years at sea, but beyond his experience in the bowels of a ship he was essentially a self-taught mechanic. After leaving the Navy he worked as a laborer at the United States Illuminating Company, then was hired by Frank J. Sprague to work on the construction of street railways. Joining the Edison General Electric Company in 1891, Emmet was an early advocate of alternating current over Thomas Edison's preferred direct current. He oversaw the design of hydroelectric generators for the Niagara falls project, and collaborated with Charles G. Curtis on development of turbine engines. In 1915 he persuaded the US Navy to test GE's turbines in place of the then-standard steam engines, leading to GE's contract to construct several new "all-electric" warships. He held nearly 200 patents, and spent many years on development of mercury vapor turbines.

Emmet was a great-grandson of Thomas Addis Emmet, an Irish revolutionary exiled in the 19th century, who came to America and became Attorney General of New York. He was a cousin of noted attorney Richard S. Emmet, and his sister Rosina "Posie" Emmet was the mother of playwright Robert E. Sherwood.